Uno strumento per analizzare l’impatto di una variazioneb nella formulazione di un quesito INVALSI di matematica = A tool for analyzing the impact of a variation in the formulation of an INVALSI question in Mathematics

In this paper we present a new methodology that allows to measure and analyse the impact of a varia-tion in the formulation of a math question on students’ responses. There are many researches on how the formulation of a question influences students’ performances in solving a task; analysing the impact of a single variation in the formulation of a task is very complex in terms of students’ resolution processes because it is not possible to administer two similar tasks to the same student without them affecting each other. The statistical tool presented allows to overcome this obstacle by means of standardized tests analysed through the Rasch model and the main statistical indices. Specifically, the article describes the statistical tool used and its validation plan, based on a study that involves about 800 students starting from an INVALSI test for grade 6 administered in 2012-13. Finally, we analyse an example of a task to highlight the potential of the methodology that we present. Such analysis is presented not only to analyse the impact of a variation in students’ performance but also to obtain educational information through a qualitative approach